Activated carbon bodies having clay binder and method of making same

ABSTRACT

A body made of activated carbon particles bonded together with a clay binder which can be attapulgite and/or sepiolite, and a plasticizing organic binder. The organic binder is more typically cellulose ether and/or cellulose ether derivative at a level of about 2 to 12 wt. % and the clay about 2% to about 30 wt % based on the carbon and clay. A method for making the body involves forming an aqueous mixture composed of the clay, organic binder and carbon, forming the mixture into a body, and drying the formed body.

This invention relates to carbon bodies which are made from mixturescontaining a clay binder which can be attapulgite and/or sepiolite. Thistype of binder when used according to the present invention improves thelow temperature strength without sacrificing their adsorption capacity,thus enabling their more effective use in gas phase low temperatureadsorption applications.

BACKGROUND OF THE INVENTION

Activated carbon materials have found use in a variety of applicationsin the gas phase such as for example radon testing, gas masks,adsorption of volatile organic compounds, etc.

The predominant commercial use for activated carbon is in the form ofgranules. While activated carbon in the form of granules can perform thedesired adsorption for many applications, there are some applications inwhich the granules have drawbacks. In some cases back pressure of apacked bed of granules is a problem. Some applications can result inconsiderable wear of the granules by attrition, causing loss of materialor bed packing. Furthermore, the fines which are generated as a resultof attrition can block the flow path.

Another approach is to use an extruded activated carbon in the form of acellular structure such as a honeycomb. The honeycomb can readily beshaped by extruding fine powders of activated carbon with suitablebinders. Such a shape allows for ease of flow of the gases through thehoneycomb with little back pressure. Also, since the honeycomb is asolid piece, there should be little or no wear or attrition of thecarbon.

In order to form an activated carbon honeycomb by extrusion, the carbonmust be in the form of a fine powder. This can then be mixed with aliquid such as water and suitable plasticizers and binders. Thisplasticized mixture is then extruded through a die into the honeycombshape, and dried.

These bodies sometimes suffer from low strength both in the as-extrudedstate and in the as-dried state. They can also develop cracks during thedrying procedure. This is especially evident in the larger bodies due todifferential shrinkage which occurs because of loss of moisture betweenthe outer surfaces and the interior of the body.

Clays have been used as binders in carbon mixtures to impart strength tothe carbon body formed therefrom.

U.S. Pat. No. 4,518,704, JP 57-122924 (1982), and 49-115110 (1974)relate to bodies containing or made of activated carbon in which claybinders are used.

It is highly desirable to improve the strength of the extruded honeycombboth in the extruded state for further processing and handling and alsoafter drying to improve performance. The present invention provides suchimproved bodies and a method for making them.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided a bodymade of activated carbon particles bonded together with a clay binderwhich can be attapulgite and/or sepiolite, and a plasticizing organicbinder. The organic binder is more typically cellulose ether and/orcellulose ether derivative at a level of about 2 to 12 wt. %, and theclay at about 2% to about 30 wt % based on the carbon and clay.

In accordance with another aspect of the invention, there is provided amethod for making the above described body, which involves forming anaqueous mixture composed of the clay, organic binder and carbon, formingthe mixture into a body, and drying the formed body.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plot of amount of clay versus the room temperature strengthof bodies of the present invention.

FIG. 2 is a plot of amount of clay versus the butane adsorption ofbodies of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The activated carbon bodies of the present invention are characterizedby having carbon particles bound together by a clay binder and aplasticizing organic binder.

The activated carbon bodies of the present invention are made by shapinga body from an aqueous mixture of activated carbon, plasticizing organicbinder, and clay which can be attapulgite clay, sepiolite clay orcombinations thereof. The body is dried.

As a result of the clay binder according to the present invention, thebodies thus produced exhibit the characteristics of high strength at lowtemperatures, that is in the as-formed and as-dried state, up totemperatures of for example, about 200° C. They also exhibit highadsorption capacity.

The type of carbon

Activated carbon is a non-graphitic microcrystalline form of carbonwhich has been processed to produce a carbon with high porosity. Themicrocrystalline areas are made up of six-member carbon rings which areseparated by areas of disorganized carbon. Activated carbon, typicallyhas a high N₂ BET surface area in the range of about 450 to about 1800m² /g. There are various types of microporosity present in activatedcarbon. One classification scheme adopted by the International Union ofPure and Applied Chemistry classifies pores according to their width asfollows: micropores which are less than about 2 nanometers, mesoporeswhich are about 2 to about 50 nanometers, and macropores which are morethan about 50 nanometers.

Activated carbon from any available source can be used, e.g., coconutshell, such as PCB-P from Calgon Carbon, Pittsburgh, Pa., wood based,such as Nuchar® available from WestVaco, Chemical Division, Covington,Va., coal based such as Calgon Carbon BPL-F3, and WPH-P. Or it can bemade from pyrolysis of organic compounds. An example of the latter ishighly sulfonated styrene/divinylbenzene ion exchange resin, such asAmbersorb® available from Rohm and Haas, Philadelphia, Pa.

Depending on the application, the nature of the activated carbon canvary as far as particle size, surface area, adsorption capacity, e.g.,for volatile organics as hydrocarbons, adsorption efficiency, porosity,pore size, etc. The carbon can be a single type or a blend of typesbased on for example, precursor source, particle size, porosity, etc.

Preferably, the activated carbon powder is a fine powder wherein themedian particle size is about 5 to about 40 micrometers in diameter asmeasured by Coulter Counter technique.

If the mixture is to be extruded into a honeycomb body, it isadvantageous that the particles have an upper limit in size which isabout one-half to about one-third the thickness of the honeycomb cellwall formed during extrusion. Some advantage may be achieved in terms ofstiffening the batch rheology by blending different particle sizedistributions.

One source of activated carbon suitable for use in this invention isBPL-F3 activated carbon available from Calgon Carbon Corp. in severalparticle sizes and at different measurements of surface area. Aparticular preferred variety of activated carbon from this source is the"6×16" mesh size, which is available at a surface area of about 1050 toabout 1300 m² /g.

Especially suited to the practice of the present invention is a mixtureof activated carbon such as Calgon Carbon BPL-F3 or Calgon Carbon WHP-P,or both, which in the practice of the present invention are ground to anaverage particle size of about 5 to about 10 micrometers in diameter,and Nuchar® SN-20 a coarser powder available from Westvaco, having anaverage particle size of about 30 to about 40 micrometers in diameter asmeasured using the Coulter Counter technique.

The clay binder

A discussion of clays is found in "An Introduction to Clay ColloidChemistry", H. van Olphen, 2nd. Ed., pp. 57-71, and "Chemistry of Claysand Clay Minerals", A. C. D. Newman, Ed., Longman Scientific &Technical, London, 1987, pp. 11-12 and 107-114. According to thesepublications, clays are layered alumino-silicates, the different classesof which are characterized structurally according to the arrangement ofordering of the layers and chemically according to the cations that arepresent such as Al, Si, Mg, Na, or Li. There are six main groups ofclays that are characterized by their structure. These groups includethe following: 1) kaolinite (kaolin), 2) pyrophyllite-talc group, 3)micas, 4) chlorites, 5) smectites and vermiculites, 6) palygorskite andsepiolite. Dioctahedral smectites are subdivided chemically intomontmorillonite, beidellite, and nontronite. Montmorillonite andbeidellite chemically are alumina rich whereas nontronite is iron rich.

The two principal building blocks which make up most clays are an atomof silicon surrounded by 4 oxygen atoms or tetrahedrally coordinated,and an aluminum or magnesium atom surrounded by six oxygen atoms orhydroxyl groups also referred to as octahedrally coordinated. Thesebuilding blocks are arranged into layers or sheets. In a silica sheet,also called a tetrahedral sheet, three of the four oxygen atoms of eachtetrahedron are shared by three neighboring tetrahedra and the fourthoxygen atom of each tetrahedron is pointed downward. For the octahedralsheet or alumina or magnesia sheet, the cation, either Al or Mg, issurrounded by oxygen or hydroxyl atoms located on the six corners of aregular octahedron.

Minerals that have a 1:1 layer structurally consist of alternatingsilica and alumina sheets. Kaolin is a 1:1 layer mineral. Chemicallykaolin has very little atom substitution into its clay structure.

The 2:1 layer minerals include pyrophyllite, talc, mica, chlorite,smectite, and vermiculite. Montmorillonite (common name is bentonite) isan example of a 2:1 layer mineral which has an alumina or magnesiumsheet surrounded on either side by a silica sheet. The uniquecharacteristic of montmorillonite clay is that when it comes intocontact with water or vapor it swells. Palygorskite (common nameattapulgite) and sepiolite are distinguished from the other layered clayminerals by having an entirely different arrangement of tetrahedral andoctahedral elements within a unit cell. (A unit cell is an arrangementof atoms in a crystalline material the shape and size of which determinethe response of the material to irradiation by x-rays. The arrangementof the atoms within the unit cell determines the relative intensity ofthe x-ray diffraction lines. The size and shape of the atoms determinesthe angular position of the diffraction lines.) The structure ofattapulgite and sepiolite does not contain a continuous octahedralsheet. Instead, the structure consists of octahedral sheets in the formof ribbons attached alternately to opposite sides of the continuoussheets of SiO₄ tetrahedra. The tetrahedra point in opposite directionsin order to coordinate with the octahedral ribbons. The structure andcomposition of the ribbon-like edge is proportionately present to a muchgreater extent than in other layered silicate structures. Thisribbon-like edge is responsible for the chemistry and properties ofattapulgite and sepiolite clay.

Attapulgite and sepiolite crystallize in the form of long needles. Openchannel structures exist within these structures which run parallel withthe edges of the ribbons and the length of the fiber axes. Thesechannels can be filled with water or absorbed ions. Attapulgite is morehighly substituted than is sepiolite. Attapulgite clay is a crystallinehydrated magnesium aluminum silicate. Attapulgite tends towards adioctahedral composition having a ratio of Mg to trivalent cationsbetween 3:1 and 1:3. Compositionally, sepiolite contains predominatelyMg in octahedral sites and is thus octahedral.

Due to the unique structure of attapulgite clay, it cannot swell apartas a montmorillonite does, for example. The presence of attapulgite clayin an activated carbon honeycomb renders the honeycomb nonreactive withwater. For example, some activated carbon honeycomb compositions madewith bentonite clay as the binder and processed using the same proceduredescribed in this application dissolve almost immediately after they areplaced in water. As the bentonite rehydrates, it swells. This swellingcauses the honeycomb to break apart. Honeycombs made with attapulgiteclay as the binder retain their shape and strength immediately afterthey are placed in water.

Attapulgite clay is a high surface area material which is also porous.The N₂ BET surface area of attapulgite clay is significantly higher thanfor the other types of clay mentioned here. The N₂ BET surface area ofattapulgite clay falls within the range of about 120 to about 150 m² /g,whereas the respective surface areas for the specific types of bentoniteand kaolin clays used in the examples in Table 1 are about 50-60 m² /gand about 7-9 m² /g.

Attapulgite clay is commercially available. It is supplied in boththermally activated form and in non-activated state. It is preferred touse the clay in the activated state because there is less cracking inthe product body. Some sources of attapulgite clay are supplied byEnglehard under the names of Attagel® 50 and Attasorb® LVM, the latterhaving a N₂ BET surface area of about 120 m² /g. Attagel® 50 is a raw ormined clay which has not been heat treated. Attasorb® LVM has beenthermally activated by a high temperature drying process, and thereforeit is the more preferred of the two.

The Organic Binder

The organic binder can be any known plasticizing organic binder, thatcontributes to the plasticity of the mixture for shaping into a body.Typical plasticizing organic binders are cellulose ether type bindersand/or their derivatives some of which are thermally gellable. The moretypical organic binders, according to the present invention aremethylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose,hydroxybutyl methylcellulose, hydroxyethylcellulose,hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethyl methylcellulose, sodium carboxymethylcellulose, and mixtures thereof. Methylcellulose and/ormethylcellulose derivatives are most typically used in the practice ofthe present invention. Methylcellulose, hydroxypropyl methylcellulose,and combinations thereof are especially preferred. Preferred sources ofcellulose ethers and/or derivatives thereof, are Methocel® A4M and20-333, F4 and F40 from Dow Chemical Co. Methocel® A4M is amethylcellulose binder having a gel temperature of 50°-55° C., and a gelstrength of 5000 g/cm² (based on a 2% solution at 65° C.). Methocel®20-333, F4, and F40 are hydroxypropyl methylcellulose.

An aqueous mixture is formed comprising in percent by weight about 2% toabout 12% of the organic binder, about 2% to about 30% of the clay, withthe balance of the mixture being activated carbon particles.

The higher the clay content, the higher is the organic binder contentrequired to impart plasticity to the mixture. Too high a clay contentinterferes with the adsorption capacity of the body.

The clay content is chosen depending on the properties which are desiredin the body.

For example, for bodies in which high strength is desired, the claycontent is relatively high. With attapulgite clay, levels of about 15%to about 30% are preferred with organic binder levels, especially thepreferred organic binders, of about 8% to about 10%.

In bodies in which high adsorption capacity is desired, the clay contentis generally lower than if strength is the predominant consideration.For high adsorption capacity, with attapulgite clay, levels of about 5%to 15% are preferred with organic binder levels, especially thepreferred organic binders, of about 5% to about 7%.

The weight percent of clay, organic binder, and water are calculated asfollows: ##EQU1##

The mixture is formed by dry blending the solid components and thenmixing with water. One technique of mixing, although it is to beunderstood that the invention is not limited to such is to place the dryblended components in a Muller mixer or other type of mixer such as asigma blade or double arm mixer. While the solids are being mixed, wateris added. Once the water is added, the Muller or other mixer is rununtil the batch compacts and becomes plasticized.

The water content in the mixture can be adjusted in order to impartoptimum plasticity and handleability to the mixture. As the mixture isbeing mixed and water is being added, a point is reached at which thewater is sufficient to wet all the particles. Continued mixing compactsthe powder by removing air, and the compacted powder starts toagglomerate into lumps. Continued mixing results in these lumps becomingplastic. Excess water makes these lumps too soft for the formingprocess. Generally, the water content is about 80% to about 150%.

In order to aid mixing, the batch can be pre-extruded one or severaltimes such as by extruding through a multi-hole strand die to effectfurther mixing and to substantially homogenize the batch mixture.

Once the mixture is observed to be well plasticized, as indicated byhand or torque rheometer, it is formed into a body.

The bodies according to the present invention can have any convenientsize and shape. For adsorption applications, the preferred shape is acellular body such as a honeycomb structure. Some examples of honeycombsproduced by the process of the present invention, although it is to beunderstood that the invention is not limited to such, are those havingabout 94 cells/cm² (about 600 cells/in²), about 62 cells/cm² (about 400cells/in²), or about 47 cells/cm² (about 300 cells/in²), those havingabout 31 cells/cm² (about 200 cells/in²), or those having about 15cells/cm² (about 100 cells/in²). Typical geometries for high capacitygas adsorption applications are the 94 cells/cm² (about 600 cells/in²),and about 62 cells/cm² (about 400 cells/in²) bodies. Wall (web)thicknesses range typically from about 0.1 to about 0.6 mm (about 4 toabout 25 mils). The external size and shape of the body is controlled bythe application and is not limited to those described above. Forexample, other combinations of cell densities and wall thicknesses canbe made.

The forming can be done by any method that makes use of shaping aplasticized mixture. The preferred method of forming is by extrusion. Aram extruder is typically used, although any extrusion equipment knownin the art can be used such as a continuous auger or twin screwextruder.

In forming honeycomb structures, it is preferred to extrude the mixturethrough a honeycomb die.

If desired, the formed body can be cut into parts of varying sizes.

The resulting formed body is then dried at temperatures not higher thanabout 125° C. to remove water. Because the bodies have a relatively highwater content due mostly to the porosity of the carbon particles, careis taken to ensure that the bodies dry slowly and evenly so that they donot crack.

Several drying procedures can be employed and the choice of proceduredepends largely on the size of the bodies being dried.

For example, small bodies, that is, bodies which have at least onedimension which is no greater than about 2.54 cm (1") can be dried bywrapping the bodies in aluminum foil and placing in a dryer set at nohigher than about 100° C., typically at about 95° C. for a sufficienttime to remove the water. The foil creates a humid environment so thatthe extruded body dries slowly and uniformly thus preventing cracking.Drying time can vary depending on the size of the body. For example, fora 2.54 cm (1") diameter, 22.9 cm (9") long honeycomb, the drying time istypically about 3 days.

Drying of large size crack-free activated carbon bodies containing morethan about 100% water in the as formed state is difficult. Large sizebodies according to the present invention are those having alldimensions greater than about 2.54 cm. For example, with honeycombs,initially, surface drying is so rapid that the bodies crack within about10 minutes when left at ambient conditions;. When water is removed fromthe surface by rapid drying, an outer ring of dried honeycomb shrinksmore than the center of the honeycomb which is still moist. Thus, themechanism for cracking is differential shrinkage between the outer ringof dried honeycomb and the interior which still contains a high level ofmoisture.

The problem of differential shrinkage causing cracking can solved byusing controlled humidity drying which accomplishes the uniform transferof moisture from the center of the honeycomb outward. The initialportion of a controlled humidity drying schedule maintains the humidityat high levels of for example >90% relative humidity. Controlledhumidity drying schedules are used for drying activated carbonhoneycombs made by the manner of this invention in sizes greater thanabout 5.08 cm (about 2") in diameter.

Controlled humidity drying can be used also for small bodies.

In accordance with a preferred embodiment, the controlled humiditydrying is done as follows.

(1) The temperature of the as-formed body is raised to a firsttemperature of no greater than about 90° C., preferably about 60° C. toabout 90° C., without allowing the body to lose moisture. This step isdone typically in a high humidity atmosphere (relative humidity ofgreater than about 90%) and mainly to prevent surface evaporation fromthe body.

(2) While the body is at the first temperature, moisture is slowlyremoved from the body until it has about 45% to about 65% by weightmoisture remaining. This step is done typically in a high humidityatmosphere. Slow removal of moisture is necessary to prevent cracking.

(3) While the body is at the first temperature, the humidity to whichthe body is exposed is lowered for the purpose of increasing the rate ofmoisture removal. This is done to drop the moisture content in the bodyto no less than about 20% by weight of the starting moisture content,and typically about 10% to about 20%.

The strength of activated carbon bodies produced by the method of thepresent invention is higher than that of bodies produced using someother well-known clay binders as will be shown in the examples thatfollow.

To more fully illustrate the invention, the following non-limitingexamples are presented. All parts, portions, and percentages are on aweight basis unless otherwise stated.

EXAMPLES 1-15

Compositions of activated carbon, clays and A4M methylcellulose weremade up as given in Table 1 below with additions of water. The percentswere based on the weight of the activated carbon and clay combined. Eachbody represented in Table 1 contained two kinds of activated carbon in aratio of about 1:4 with WestVaco Nuchar® SN-20 being the activatedcarbon present in the lower amount and Calgon Carbon's BPL-F3 ground toabout-200 mesh being the activated carbon present in the larger amount.The clays were bentonite, kaolin, and attapulgite being respectively,G-129 from Kaopolite, Inc., Glomax LL from Dry Branch Kaolin, andAttasorb® LVM. Honeycombs measuring about 2.54 cm (1") in diameter andhaving about 31 cells/cm² (200 cells/in²), and a wall thickness of about0.4 mm (15 mil) were extruded with the compositions of Table 1. Eachhoneycomb was wrapped in aluminum foil and dried at about 95° C. forabout 3 days. Crushing strengths and adsorption capacity were measuredas described below.

Crushing strengths are measured in a compression tester made by TiniusOlsen at a cross head rate of about 2.54 mm (about 0.1")/min. Eachsample number reported is an average of measurements on six differentpieces. Strengths were measured at room temperature on the samplesas-dried.

Butane adsorption capacity was measured by placing test samples in aVycor® tube housed inside a tube furnace having inlet and outlet ports.A 1500 volume ppm butane gas stream in a nitrogen carrier gas wasintroduced to the sample at a flow rate of about 4,000 cc/min. andadsorption was measured by monitoring the exit gas stream with a flameionization detector. Adsorption at room temperature was consideredcomplete when the calibrated detector reading had reached about 95%. Atthis time, the inlet gas stream was changed to nitrogen and desorptionof the butane at room temperature was measured. When the detectorreading reached a value of about 5%, the temperature of the sample wasraised to about 100° C. by increasing the furnace temperature to removethe rest of the butane adsorbed on the sample. The detector readingswere plotted versus time and the adsorption and desorption were measuredby integrating the area of each curve. The values reported foradsorption are the milligrams of butane adsorbed divided by the samplemass after testing.

The strengths and adsorption capacities for each composition are givenin Table 1 and plotted in FIGS. 1 and 2 respectively. The results showthat the strength values for the compositions with the attapulgite clayare higher for a given clay and organic binder content, as shown bydirect comparison of Nos. 1, 6, and 11, and 4, 9, and 14. Adsorptioncapacity is comparable for these clays at a given level of clay. As theclay binder and organic binder content increase, the adsorption capacityfalls off somewhat. Therefore, depending on what properties are desired(strength or adsorption capacity, or a combination of both) in theproduct body, the most effective combination of binders can be chosen.

                  TABLE I                                                         ______________________________________                                                     Organic          Dried   Butane                                       Clay    Binder    Water  Strength                                                                              Adsorption                              No.  (%)     (%)       %      PSI     mg/g                                    ______________________________________                                        BENTONITE                                                                      1    5      6         135     791    61.4                                     2   15      6         133    1242    46.4                                     3   20      6         120    1231    42.1                                     4   25      8         112    1572    29.7                                     5   30      8         119    1830    28.3                                    KAOLIN                                                                         6    5      6         134     751    61.3                                     7   15      6         124     869    55.9                                     8   20      6         116     949    49.4                                     9   25      8         110    1650    47.8                                    10   30      8         105    1801    42.0                                    ATTAPULGITE                                                                   11    5      6         143    1442    59.2                                    12   15      8         129    2217    51.8                                    13   20      8         121    2607    43.1                                    14   25      8         120    2813    40.1                                    15   30      10        118    3599    35.7                                    ______________________________________                                    

EXAMPLE 16

An extrusion was made with a mixture of about 78.4% Calgon Carbon WPH-P,and about 19.6% WestVaco Nuchar SN20, about 2% Englehard Attasorb® LVM,and about 6% Dow Chemical Co. K75M methocel. This mixture was mixed withabout 85% water and extruded into 2.54 cm diameter honeycombs having ageometry of about 15 cells/cm² (about 100 cells/in²), and wall thicknessof about 0.6 mm (25 mil). Drying of the honeycombs was done by wrappingthe samples in aluminum foil and placing them in a dryer at about 100°C. for 3 days. The crushing strength was about 1090 psi. The adsorptioncapacity was measured using the procedure described above with a flowrate of about 2,000 cc.min. The adsorption capacity was about 70.1 mgbutane/g of sample., This example illustrates high adsorption capacitywith a low clay addition. The reasonable strength of 1090 psi at thislow clay addition is due to the thickness of the honeycomb wall.

It should be understood that while the present invention has beendescribed in detail with respect to certain illustrative and specificembodiments thereof, it should not be considered limited to such but maybe used in other ways without departing from the spirit of the inventionand the scope of the appended claims.

What is claimed is:
 1. A method for making a carbon body, said method consisting essentially of:a) forming an aqueous mixture comprising about 2% to 30attapulgite clay, about 2% to 12% plasticizing organic binder selected from the group consisting of methylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose, hydroxybutyl methylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, sodium carboxy methylcellulose, and mixtures thereof, and the balance being activated carbon particles; b) forming said mixture into a body; and c) drying the formed body.
 2. A method of claim 1 wherein the median particle size of the carbon is about 5 to about 40 micrometers in diameter as measured by Coulter Counter technique.
 3. A method of claim 1 wherein the organic binder is selected from the group consisting of methylcellulose, hydroxypropyl methylcellulose, and combinations thereof.
 4. A method of claim 1 wherein the attapulgite clay content is about 5% to about 15%.
 5. A method of claim 4 wherein the organic binder content is about 5% to about 8%.
 6. A method of claim 1 wherein the attapulgite clay content is about 15% to about 30%.
 7. A method of claim 6 wherein the organic binder content is about 8% to about 10%.
 8. A method of claim 1 wherein the forming is done by extruding the mixture.
 9. A method of claim 1 wherein the body is formed into a honeycomb structure.
 10. A body comprised of activated carbon particles bonded together with about 2% to 30% by weight attapulgite clay binder and about 2% to 12% plasticizing organic binder selected from the group consisting of methylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose, hydroxybutyl methylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, sodium carboxy methylcellulose, and mixtures thereof.
 11. A body of claim 10 wherein the median particle size of the carbon is about 5 to about 40 micrometers in diameter as measured by Coulter Counter technique.
 12. A body of claim 10 wherein the organic binder is selected from the group consisting of methylcellulose, hydroxypropyl methylcellulose, and combinations thereof.
 13. A body of claim 10 wherein the attapulgite clay content is about 5% to about 15%.
 14. A body of claim 10 wherein the organic binder content is about 5% to about 8%.
 15. A body of claim 10 wherein the attapulgite clay content is about 15% to about 30%.
 16. A body of claim 15 wherein the organic binder content is about 8% to about 10%.
 17. A body of claim 10 having a honeycomb structure. 